Deep winter intrusions of urban black carbon into a canyon near Santiago, Chile: A pathway towards Andean glaciers

• Published in: Environmental pollution (1987) 2021-12, Vol.291, p.118124-118124, Article 118124
• Main Authors: Huneeus, Nicolás, Lapere, Rémy, Mazzeo, Andrea, Ordóñez, César, Donoso, Nicolás, Muñoz, Ricardo, Rutllant, José A.
• Format: Article
• Language: English
• Subjects: Andean cryosphere; Atmospheric transport; Light-absorbing particles; Mega-city pollution; Mountain-valley circulation
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2021.118124

Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows. •Transport of urban BC in deep, dense layers is found far into an Andean canyon.•A return flow in an elevated secondary layer is observed with valley intrusions.•Air pollutants transported into the canyon are from the vicinity of its entrance.•Climatologically, intrusions into the canyon occur 90% of the wintertime days.•Cloud cover prevents air masses flow towards the Andes 10% of winter days.